Air flow control system and uses thereof in apparatus for combustion of solid fuels

ABSTRACT

Air flow control systems for use in the combustion of solid fuel are provided. Such air flow control systems may be used in a combustion apparatus, such as a cook stove. The use of such air flow control systems in the combustion apparatus can efficiently combust solid fuels with low emission of particulate matter and harmful gases.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 62/834,262, filed Apr. 15, 2019, which is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates generally to combustion of solid fuels, and more specifically to an air flow control system suitable for use with cook stoves to improve combustion of solid fuels.

BACKGROUND

A large portion of the world's population relies on solid fuels for cooking, such as collected woody sticks. These fuels are frequently burned using indoor cook stoves, which release smoke and other harmful compounds (e.g., carbon monoxide). This can be a significant health and safety hazard, causing illness and premature death in populations that have few cooking or heating alternatives. Thus, there is a need for cook stoves which can burn solid fuels such as biomass with lower emission of particulate matter and harmful gases.

BRIEF SUMMARY

The present disclosure addresses this need by providing an air flow control system designed for use with a combustion apparatus, such as a cook stove. The use of such air flow control system in cook stoves unexpectedly improves performance in the combustion of solid fuels, for example, with respect to thermal efficiency, particulate matter levels and carbon monoxide levels.

In some aspects, provided is an air flow control system that includes an air source and an air flow housing unit. In some embodiments, the air source outputs pressurized air. In some embodiments, the air flow housing unit is a hollow, enclosed unit. The air flow housing unit has a surface with at least one air outlet. In some variations, the top surface has the at least one air outlet. In some embodiments, the air flow housing unit receives pressurized air from the air source, and releases air from the interior to the exterior of the air flow housing unit through the at least one air outlet. In some variations, the air flow housing unit receives pressurized air from the air source, and releases air from the hollow interior to the exterior of the air flow housing unit through the at least one air outlet. In some embodiments, the air flow housing unit is connected to the air source by a connector, which may be rigidly or flexibly attached to the air flow housing unit. In some embodiments, the air source and the air flow housing unit form a single module within the system. In some embodiments, the air source and the air flow housing unit are separate, detachable modules. In other embodiments, the system also includes a power source. In some variations, the air source and the power source form an air-power unit. In one variation, the air-power unit and the air flow housing unit are separate, detachable modules in the system. In another variation, the air-power unit and the air flow housing unit are integrated into a single module in the system.

In other aspects, provided is a combustion apparatus that includes a combustion chamber, and any of the air flow control systems described herein. In some embodiments, at least a portion of the air flow housing unit in the air flow control system is positioned inside the combustion chamber, and the air flow housing unit holds solid fuel on the top surface of the air flow housing unit. In some embodiments, the combustion apparatus is a cooking apparatus. In other embodiments, at least a portion of the air flow housing unit in the air flow control system is positioned below or near the combustion chamber. In one variation, the cooking apparatus is a cook stove. In other embodiments, the air flow control systems described herein may be used with, or integrated into, other household or industrial applications where heat/energy is generated from combustion.

In yet other aspects, provided is a method for burning solid fuel using a combustion apparatus that incorporate the air flow control systems described herein. In some embodiments, the method includes: placing solid fuel on the air flow housing unit of the air flow control system in the combustion apparatus, wherein at least a portion of the solid fuel is placed over at least a portion of the air outlets on the air flow housing unit; igniting at least a portion of the solid fuel; turning on the air source to (i) provide air through the air flow housing unit, and (ii) output the air through the plurality of air outlets on the air flow housing unit; and creating a fire from burning of the solid fuel.

In some variations of the foregoing systems and methods, the solid fuel comprises wood, charcoal or other forms of biomass. In certain variations, the solid fuel comprises urban waste (e.g., paper, cardboard, or sawdust) or agricultural waste (e.g., animal processing waste, or cellulosic materials). Any combination of the foregoing solid fuels may also be used.

DESCRIPTION OF THE FIGURES

The present application can be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals.

FIGS. 1A-1D depict an exemplary air flow control system that includes an air flow housing unit and an air-power unit, which are connected by an air hose. FIGS. 1B and 1C depict views inside the air-power unit shown in FIG. 1A. Specifically, FIG. 1B shows the air fan, and FIG. 1C shows the battery (e.g., rechargeable battery). FIG. 1D depicts a cross-sectional view of the exemplary air flow control system, and shows the air flow from the air fan through the air hose into the air flow housing unit.

FIG. 2A depicts an exemplary air flow housing unit with air outlets on the top surface of the unit. FIG. 2B depicts a cross-sectional view of the exemplary air flow housing unit, showing air flow into the air flow housing unit (from the air hose connected to the air flow housing unit) and air flow out of the air outlets.

FIG. 3 depicts another exemplary air flow control system that includes an air flow housing unit with an air source that is positioned above the air flow housing unit.

FIG. 4A depicts one configuration in which solid fuel may be placed in a side loading configuration on top of an air flow housing unit in an exemplary air flow control system. FIG. 4B depicts an exemplary cook stove that uses the air flow control system of FIG. 4A.

FIG. 5A depicts another configuration in which solid fuel may be placed in a front loading configuration on top of an air flow housing unit in an exemplary air flow control system. FIG. 5B depicts another exemplary cook stove that uses the air flow control system of FIG. 5A.

FIGS. 6A and 6B are photographs depicting the use of an air flow control system in a cook stove. FIG. 6A depicts the use of wood (e.g., sticks, branches) as the solid fuel. FIG. 6B depicts the use of the air flow control system in a cook stove to heat up a pot of water.

FIGS. 7A-7D are photographs depicting the use of an air flow control system in traditional mud stoves.

FIGS. 8A-8D are photographs of an air flow control system set up for use in Example 1 described herein.

DETAILED DESCRIPTION

The following description sets forth exemplary methods, parameters and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments.

In some aspects, provided are air flow control systems suitable for use in a combustion apparatus, such as a cooking apparatus. For example, the air flow control systems may be used with manufactured stoves, traditional mud and ceramic stoves, and three stones fire. The air flow control systems are also suitable for use with other household or industrial applications where heat/energy is generated from combustion.

The air flow control systems provided help achieve high efficiency in the combustion of fuels, such as wood, charcoal and other biomass. The biomass may include, for example, agricultural waste, briquettes made from agricultural waste, or other organic waste, such as urban waste. Such air flow control systems can help to minimize emissions, including, for example, particulate matter, carbon monoxide, and other products resulting from incomplete combustion that can harm health, or/and environment. Such air flow control systems can also help to maximize heat transfer efficiency, for example, by minimizing heat and/or energy losses; as well as maximize combustion efficiency, for example, by achieving low emissions and high thermal efficiency. Such combustion efficiency may be achieved with no or minimal impact on usability, ease of use (e.g., starting fires, loading fuel, tending fuel, and controlling power).

In some aspects, provided is an air flow control system that includes an air flow housing unit that receives pressurized air from an air source, and outputs the air from the interior to the exterior of the air flow housing unit where the solid fuel is positioned. The system may also include a power source to power the air source.

In other aspects, provided is also a combustion apparatus that utilizes the air flow control system described herein. In some embodiments, the combustion apparatus include a combustion chamber, and the air flow control system is positioned inside the combustion chamber. In some variations, the air flow housing unit of the air flow control system holds the solid fuel on the top surface of the air flow housing unit inside the combustion chamber. In other embodiments, the combustion apparatus include a combustion chamber, and the air flow control system is positioned below the combustion chamber. In some variations, the air flow housing unit of the air flow control system holds the solid fuel on the top surface of the air flow housing unit below the combustion chamber.

In yet other aspects, provided is also a method of burning solid fuel using the combustion apparatus and air flow control system described herein. In some embodiments, the method includes placing solid fuel on the air flow housing unit of the air flow control system in the combustion apparatus, wherein at least a portion of the solid fuel is placed over at least a portion of the air outlets on the air flow housing unit; igniting at least a portion of the solid fuel; turning on the air source to provide air through the air flow housing unit, and to output the air through the plurality of air outlets on the air flow housing unit; and creating a fire from burning of the solid fuel.

The use of the air flow control system described herein with a combustion apparatus unexpectedly improves performance of combustion, for example, with respect to thermal efficiency, particulate matter levels, and carbon monoxide levels.

The air flow control system, the combustion apparatus, and the method of using the foregoing are described in further detail below.

Air Flow Control Systems

Generally, the air flow control systems provided include an air source that outputs pressurized air, and an air flow housing unit that serves as a conduit for the pressurized air to travel from the air source to a combustion chamber.

With reference to FIG. 1A, system 100 is an exemplary air flow control system that includes air flow housing unit 102 connected by air hose 106 to air-power unit 108. Air holes 104 are located on the top surface of air flow housing unit 102. Air inlets 110 is present to draw air from the surroundings into air-power unit 108, where the air is pressurized and directed towards air flow housing unit 102.

With reference to FIG. 1B, a cross-sectional view of air-power unit 108 is depicted showing air source 112 inside air-power unit 108. Air source 112 in exemplary system 100 is a fan. In other variations, other suitable air sources may be used. Air source 112 can draw air from the surrounding into air-power unit 108 through air inlets 110 (depicted in FIG. 1A), pressurize the air, and direct the pressurized air towards air flow housing unit 102.

With reference to FIG. 1C, another cross-sectional view of air-power unit 108 is depicted showing battery 114. In some variations, the battery is a rechargeable battery.

With reference to FIG. 1D, a cross-sectional view of system 100 is depicted, which shows the air flow from air source 112 through air hose 106 into air flow housing unit 102.

With reference to FIG. 2A, the pressure air enters through the side of air flow housing unit 102. With reference to FIG. 2B, a cross-sectional view of air flow housing unit 102 is depicted, showing air flow out from the interior the air flow housing unit 102 to the exterior of the unit.

Although one exemplary configuration of the air flow control system is depicted in FIGS. 1A-1D, it should be understood that in other variations, other configurations of the air flow control system are envisioned. With reference to FIG. 3, system 300 is another exemplary air flow control system that includes air source 312 positioned above air flow housing unit 302. Air source 312 outputs air 330 into opening 320 on the top surface of air flow housing unit 302. The air flows through the interior of air flow housing unit 202 and is released through air outlets 304 on the top surface of air flow housing unit 302, at an end opposite to opening 306. Although not depicted in FIG. 3, solid fuel is placed on the top surface of air flow housing unit 302, and air 332 is output from air flow housing unit 302 to help with combustion of the solid fuel.

Other variations of the air flow control systems, and the units therein and their configurations are described in further detail below.

Air Flow Housing Unit

The air flow housing unit in the air flow control system may be made of any suitable metal. The air flow housing unit in the air flow control system may also be any suitable shape. The shape of the air flow housing unit may also vary depending on the combustion apparatus. In some embodiments, the air flow housing unit has a top surface, a bottom surface and one or more side surfaces. For example, in some variations, the air flow housing unit may be in the shape of an enclosed box, as depicts in FIGS. 1A-1D, 2A-2B and 3. In such variations, the air flow housing unit has a top surface, a bottom surface, and four side surfaces.

At least one surface of the air flow housing unit has at least one air outlet. In some embodiments, the top surface of the air flow housing unit has at least one air outlet. In some variations, at least one air outlet is positioned at the end of the air flow housing unit opposite to the end from which the pressurized air enters the interior of the air flow housing unit.

The number of air outlets, as well as the geometry, size and shape of the air outlets may vary, and affect the output of air from the interior to the exterior of the air flow housing unit. The geometry, size and/or shape of the air outlets may impact certain aspects of combustion performance. The air outlets on the air flow housing unit are configured to optimize air flow, and deliver pressurized air at optimal velocity, flow rate, direction, and location into a combustion chamber.

In some variations, the air flow housing unit has a plurality of air outlets. When there is more than one air outlet, in certain variations, the air outlets are evenly spaced. In other variations, the air flow housing unit has a single air outlet.

In some embodiments, each outlet is a hole. In certain variations, the hole is a flat hole or a formed hole. In other embodiments, each outlet is a slot. In yet other embodiments, each outlet is an air nozzle or an air jet. The air nozzles and air jets can also control the release of air from the interior to the exterior of the air flow housing unit.

In some embodiments, each air outlet has a diameter between 0.05 mm and 20 mm, between 0.1 mm and 50 mm, between 1 mm and 100 mm, at least 0.01 mm, at least 0.1 mm, at least 1 mm, or at least 100 mm. In some variations of the foregoing, the diameter is an average diameter.

In one embodiment when an air nozzle is used, compressed air flow may be amplified. Compressed air may be ejected through a series of nozzles on the outer perimeter. As the air travels along the outer wall of the nozzle, surrounding air is entrained into the stream. The airstream that results may be a high volume, high velocity blast of air at minimal consumption.

In another embodiment when an air jet is used, a small amount of compressed air may be throttled through an internal ring nozzle above sonic velocity. A vacuum may be produced, pulling surrounding or ‘free’ air through the jet. Both the outlet and inlet of the air jet may be ducted for remote position.

Air Source

The air source draws air from the surroundings, pressurizes the air, and directs the pressurized air to the interior of the air flow housing unit. In some variations, the air source is a fan. The fan may include one or more blades.

Other suitable air sources that can output a stream of pressurized air may be employed. For example, in other variations, the air source is an air pump. In one variation, the air source is a manual air pump. In some variations, the air source is a piston pump. In another variation, the air source comprises a manual air pump and air bag. In some variations, the air source is a compressed air container.

The pressurized air can enter the air flow housing unit from any direction. The air source may be positioned above, below or at the level of the air flow housing unit. For example, as depicted in FIG. 3, the air source is positioned above the air flow housing unit. In such variation, the air flow control system may further include a framework to hold the air source in place.

In other variations, the air source may also be positioned within the air flow housing unit. For example, as depicted in another exemplary air flow control system in FIG. 6A, the air source is incorporated to the bottom of the air flow housing unit.

Connector

In some variations, the system may include a connector to channel pressurized air from the air source (or air-power unit, as the case may be) to the interior of the air flow housing unit. For example, with reference again to FIGS. 1A-1D, a connector is present as depicted in system 100.

In some variations where a connector connects the air source to the air flow housing unit, the air source may be rigidly or flexibly attached to the air flow housing unit. While air hose 106 is depicted in the exemplary air flow control system in FIGS. 1A-1D, in other variations, the connector is a joint.

In other variations, with reference to FIG. 3, system 300 does not include a connector to channel the pressurized air into the air flow housing unit. The air source may be positioned close enough to direct the pressurized air into the interior of the air flow housing unit through one or more openings in the air flow housing unit.

Power Source

In some embodiments, the air source is powered by a power source. In some variations, the power source is a battery, optionally with a battery charger. In other variations, the power source comprises photovoltaic solar panels. In yet other variations, electrical power generated by heat from the stove fire may be used to power the air source, or charge the power source (e.g., battery). In some embodiments, the power source provides grid powder or solar power, or any combination thereof.

The power source may be external or internal to the system. In certain embodiments, the power source may be external, relative to the air flow housing unit and air source. In certain embodiments, the power source may be integrated into the air flow housing unit. In yet other embodiments, the power source may be integrated into the air source to form an air-power unit.

For example, in one variation, the air flow control system uses a standalone air source that may include the air source and power source, which forms an air-power unit. In another variation, the air flow control system is a single module in which the air flow housing unit is integrated with the air unit or air-power unit. In yet another variation, the air flow housing unit is a separate module from the air unit or air-power unit.

In variations where the air flow housing unit and the air-power unit are separate modules, such configuration presents several advantages. For example, when a rechargeable power source is used (e.g., a rechargeable battery), the power source can more easily be recharged by only moving the air-power module for charging. This can be helpful in rural areas where the air flow control systems may be deployed since there may not be any power plugs in kitchen, and it is dangerous and/or unpleasant to have electrical wire on the kitchen floor.

Moreover, in variations where the air flow housing unit is connected to the air-power unit by a connector, the connector creates an additional thermal barrier between the two modules, to protect the air source and power source from the heat of the combustion chamber.

The modularity of the air flow control systems provided also allows for assembly of the air-power unit in different orientations, to allow incoming air to fan, to come from different directions (e.g., from bottom, top, or side). The air flow control systems can also be adapted to the specific design/configuration of the combustion apparatus.

Air Flow

The air flow into and out of the air flow control system may be a function of one or more variables, including for example, air pressure, air flow housing unit geometry, number of air outlets, and the air outlet geometry.

In some variations, the air flow into the air flow housing unit is a function of the air source specifications, the voltage applied, as well as the load. The load may include considerations related to the air flow housing unit flow load, which may be a function of the air flow housing unit geometry. The load may also include the air outlet design, which may be impacted by the geometry (holes, air jets, air nozzles), number of air outlets, location of air outlets, and the angle of the outlet (e.g., the angle of air jets or nozzles).

In some variations, the air flow out of the air flow housing unit is a function of air mass flow rate, air flow velocity, and the power consumed by the air source.

In certain variations, the system is configured to output air at an air flow rate between 0.01 m³/min and 100 m³/min. In certain variations, the system is configured to output air at an air pressure between 1 mm-H₂O and 1000 mm-H₂O. In certain variations, the system is configured to output air at an outlet air velocity between 0.1 m/s and 10 m/s. In certain variations, the system is configured to output air at any combination of the air flow rate, air pressure and air velocity described above.

In some embodiments, the air flow control systems provided deliver air to fuel where it has maximal impact: directly burning fuel and below burning fuel. In terms of directly burning, the air flow control systems can create maximal turbulence and mixing, which generate better and more complete combustion, and higher combustion temperature, at the source of combustion (where combustion starts). The time/distance between the fuel and pot gives now enough time to burn/complete more of the combustion. In terms of below burning fuel, the air flow control systems can achieve combustion in direction of natural draft, which can help to minimize air draft loss.

In some embodiments, the air flow control systems provided herein deliver air at high velocity, which helps to achieve maximal turbulence for more complete combustion. The air flow control systems provided also allow for control of air flow rate, which can help to provide optimal air intake. Too much air can cool off the fire and result in slow and incomplete combustion; and not enough air can result in incomplete combustion.

Further, by delivering air under the fuel, the air flow control systems provided can help to minimize impact on usability as air flow requirement does not come in the way of starting fire, loading fuel, tending fire. The air flow control systems can also help to minimize need to design complicated and expensive air flow paths inside stove, and tooling for these air flow paths inside the combustion apparatus.

Combustion Apparatus

The air flow control systems described herein may be used in any suitable combustion apparatus. In preparing the air flow control system for use in a combustion apparatus, solid fuel is placed on the top surface of the air flow housing unit of the air flow control system. The solid fuel may be positioned in a side loading configuration, as depicted in FIG. 4A, or in a front loading configuration, as depicted in FIG. 5A. In the side loading configuration, the air flow housing unit may be inserted from the side of the cook stove, as depicted in FIG. 4B. In the front loading configuration, the air flow housing unit may be inserted from the front of the cook stove, as depicted in FIG. 5B.

Thus, in one embodiment, the combustion apparatus is a cooking apparatus, such as a cook stove. Suitable stoves compatible with the air flow control systems provided herein include, for example, manufactured stoves, and traditional mud and ceramic stoves. In other embodiments, the combustion apparatus is a three stones fire, which refers to the using of stones to lift and support the pot or other vessel to be heated. In one variation, with reference to FIGS. 6A and 6B, the combustion apparatus depicted therein is a manufactured stove, used to heat a pot of water (FIG. 6B). In another variation, with reference to FIGS. 7A-7D, the combustion apparatus depicted therein is a traditional mud stove, used to also heat a pot of water (FIG. 7D).

In other embodiments, the air flow control systems are used with other household or industrial applications where heat/energy is generated from combustion.

Combustion Performance

In some variations, high power thermal efficiency is the efficiency when a combustion apparatus, such as a cook stove, is used in the high cooking power mode. Thermal efficiency is expressed as a ratio of cooking power (energy into the pot) divided by fire power (energy released by the fuel). In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average high power thermal efficiency of at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, or at least 50%; between 20% and 40%, between 25% and 45%, between 30% and 50%, or between 30% and 40%. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average high power thermal efficiency at least 10% higher than, at least 20% higher than, at least 30% higher than, at least 40% higher than, at least 50% higher than, at least 60% higher than, at least 70% higher than, at least 80% higher than, at least 90% higher than, or at least 100% higher than the average high power thermal efficiency when using the combustion apparatus without the air flow control system described herein.

In some variations, low power specific consumption is the amount of fuel required to boil (or simmer) one liter of water for one minute. This metric may be used to describe the lower power (simmer) phase of testing a combustion apparatus, such as a cook stove. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average low power specific consumption of less than 0.02 MJ/min/L, less than 0.015 MJ/min/L, less than 0.1 MJ/min/L, less than 0.05 MJ/min/L, or less than 0.01 MJ/min/L. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average low power specific consumption at least 10% lower than, at least 20% lower than, at least 30% lower than, at least 40% lower than, at least 50% lower than, at least 60% lower than, or at least 70% lower than the average low power specific consumption when using the combustion apparatus without the air flow control system described herein.

In some variations, high power carbon monoxide is the CO emission per unit of energy delivered to the cooking pot. The energy delivered to the cooking pot is the total energy consumed multiplied by the thermal efficiency. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average high power carbon monoxide level of less than 3 g/MJd, less than 2.5 g/MJd, less than 2 g/MJd, less than 1.9 g/MJd, less than 1.8 g/MJd, less than 1.7 g/MJd, less than 1.6 g/MJd, less than 1.5 g/MJd, less than 1.4 g/MJd, less than 1.3 g/MJd, less than 1.2 g/MJd, less than 1.1 g/MJd, or less than 1 g/MJd; between 0.5 g/MJd and 1.5 g/MJd, or between 1 g/MJd and 2 g/MJd. The units of g/MJd carbon monoxide express grams of carbon monoxide per Mega Joule of heat delivered to a cooking utensil, such as a pot. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average high power carbon monoxide level at least 10% lower than, at least 20% lower than, at least 30% lower than, at least 40% lower than, at least 50% lower than, at least 60% lower than, at least 70% lower than, at least 80% lower than, or at least 90% lower than the average high power carbon monoxide level when using the combustion apparatus without the air flow control system described herein.

In some variations, low power carbon monoxide is the carbon monoxide emission per liter of water simmered per minute. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average low power carbon monoxide level of less than 0.4 g/min/L, less than 0.35 g/min/L, less than 0.3 g/min/L, less than 0.25 g/min/L, less than 0.2 g/min/L, less than 0.15 g/min/L, or less than 0.1 g/min/L. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average low power carbon monoxide level at least 10% lower than, at least 20% lower than, at least 30% lower than, at least 40% lower than, at least 50% lower than, at least 60% lower than, at least 70% lower than, at least 80% lower than, or at least 90% lower than the average low power carbon monoxide level when using the combustion apparatus without the air flow control system described herein.

In some variations, high power particulate matter is the particulate matter emission per unit of energy delivered to the cooking pot. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average high power particulate matter level of less than 300 mg/MJd, less than 250 mg/Mk, less than 200 mg/MJd, less than 150 mg/MJd, less than 100 mg/MJd, less then 95 mg/MJd, less than 90 mg/MJd, less than 85 mg/Mk, less than 80 mg/MJd, less than 75 mg/Mk, or less than 80 mg/Mk; or between 50 mg/Mk. and 100 mg/Mk, or between 60 mg/Mk. and 100 mg/Mk. The units of mg/MJd particulate matter express milligrams of particulate matter per Mega Joule of heat delivered to a cooking utensil, such as a pot. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average high power particulate matter level at least 10% lower than, at least 20% lower than, at least 30% lower than, at least 40% lower than, at least 50% lower than, at least 60% lower than, at least 70% lower than, at least 80% lower than, or at least 90% lower than the average high power particulate matter level when using the combustion apparatus without the air flow control system described herein.

In some variations, low power particulate matter is the particulate matter emission per liter of water simmered per minute. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average low power particulate matter level of less than 20 mg/min/L, less than 15 mg/min/L, less than 10 mg/min/L, less than 5 mg/min/L, less than 4 mg/min/L, or less than 3 mg/min/L. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average low power particulate matter level at least 10% lower than, at least 20% lower than, at least 30% lower than, at least 40% lower than, at least 50% lower than, at least 60% lower than, at least 70% lower than, at least 80% lower than, or at least 90% lower than the average low power particulate matter level when using the combustion apparatus without the air flow control system described herein.

In some variations, indoor emissions carbon monoxide is the high power or low power CO emission rate into the kitchen, whichever is greater. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average indoor emissions carbon monoxide level of less than 5 g/min, less than 1 g/min, less than 0.5 g/min, or less than 0.35 g/min. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average indoor emissions carbon monoxide level at least 1% lower than, at least 3% lower than, at least 10% lower than, at least 20% lower than, at least 30% lower than, at least 40% lower than, or at least 50% lower than the average indoor emissions carbon monoxide level when using the combustion apparatus without the air flow control system described herein.

In some variations, indoor emissions particulate matter is the high power or low power PM2.5 emission rate into the kitchen, whichever is greater. It is calculated in the same manner as the indoor emissions carbon monoxide except a factor of 1000 is added to convert grams to milligrams. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average indoor emissions particulate matter level of less than 30 mg/min, less than 20 mg/min, less than 15 mg/min, less than 10 mg/min, or less than 5 mg/min. In some embodiments, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has an average indoor emissions particulate matter level at least 10% lower than, at least 30% lower than, at least 50% lower than, at least 70% lower than, or at least 90% lower than the average indoor emissions particulate matter level when using the combustion apparatus without the air flow control system described herein.

It should be understood that the phrase “A is at least x% higher than B” refers to A being (1+x%) times B or more. For example, if A is least 20% higher than B, A is 1.2B or more. Similarly, the phrase “A is at least x% lower than B” refers to A being (1−x%) times B or less. For example, if A is at least 20% lower than B, A is 0.8B or less.

In some variations, combustion of the solid fuel in a combustion apparatus using the air flow housing unit described herein has any combination of the average high power thermal efficiency, average low power specific consumption, average high power carbon monoxide level, average low power carbon monoxide level, average high power particulate matter level, average low power particulate matter level, average indoor emissions carbon monoxide level, and average indoor emissions particulate matter level described above.

Solid Fuel

In some variations, the solid fuel used with the air flow control system and combustion apparatus described herein comprises biomass. The biomass may be lignocellulosic biomass, including wood, branches, sticks, agricultural waste, foliage, or any combinations thereof. In some variations, the solid fuel comprises wood.

In some variations, the solid fuel also comprises at least 10% water, at least 20% water, or between 10% and 20% water.

In other variations, the solid fuel includes urban waste and/or agricultural waste. Urban waste may include, for example, paper, cardboard, and/or sawdust. Agricultural waste may include, for example, animal processing waste (e.g., manure) and/or cellulosic materials (e.g., rice husks, corn, corn cobb, coffee husk, sugar cane waste, pine needles, dry leafs, or other forest waste). The solid fuel may be made up of a combination of waste materials.

In some embodiments, the solid fuel may also be used in the form of briquettes. In certain variations, the briquettes used may be hand-pressed. The waste materials described above can be mixed and compressed into a briquette using a briquette press or a lever system. In some variations, the briquettes used are made from urban waste, for example, ⅓ paper, ⅓ cardboard, ⅓ saw dust. These materials can be soaked in water for 24 hours to become soft and easy to mix, and then mixed while wet. Once mixed, they can be placed in molds to be pressed to expel extra water and increase density. Last, the briquettes can be left to dry in the sun for few days to gain strength and to minimize humidity in the briquettes.

In other embodiments, the solid fuel is used with minimal processing. The combustion apparatus may be configured to allow feeding of large pieces of solid fuel, such as long sticks or branches, into the apparatus without requiring the fuel be broken up in to small pieces. However, it should be understood that in other embodiments, solid fuel such as biomass may undergo processing prior to use with the combustion apparatus or method as described herein. This processing may include, for example, chopping, cutting, or otherwise breaking into smaller pieces, stripping branches of leaves or pressing pieces of fuel together.

In one variation, the hand-pressed briquettes used have a lower density than other solid fuel sources such as wood or industrial briquettes. For example, wood has a density of about 0.6 g/cm³. Industrial briquettes that are mechanically compressed and typically have a density of at least 1 g/cm³. In contrast, the briquettes used herein have a lower density. In some embodiments, the briquettes have a density less than 0.6 g/cm³. In other embodiments, the briquettes have a density between 0.1 g/cm³ and 0.5 g/cm³. In an exemplary embodiment, the briquettes have a density about 0.3 g/cm³. It should be understood, however, that the method and apparatus described herein may burn briquettes made using any methods known in the art, including, for example, industrial briquettes.

ENUMERATED EMBODIMENTS

The following enumerated embodiments are representative of some aspects of the invention.

1. An air flow control system, comprising:

-   -   an air source configured to output pressurized air; and an air         flow housing unit,         -   wherein the air flow housing unit is a hollow, enclosed             unit,         -   wherein the air flow housing unit has a top surface with at             least one air outlet, and wherein the air flow housing unit             is configured to (i) receive pressurized air from the air             source, and (ii) release air from the hollow interior to the             exterior of the air flow housing unit through the at least             one air outlet.

2. The system of embodiment 1, wherein the air flow housing unit is connected to the air source.

3. The system of embodiment 2, wherein the air flow housing unit is connected to the air source by a connector.

4. The system of embodiment 3, wherein the connector is rigidly attached to the air flow housing unit.

5. The system of embodiment 3, wherein the connector is flexibly attached to the air flow housing unit.

6. The system of embodiment 3, wherein the connector is a hose or a joint.

7. The system of any one of embodiments 3 to 6, wherein the connector creates a thermal barrier between the air source and the air flow housing unit.

8. The system of any one of embodiments 1 to 7, wherein the air source is a fan, a compressed air container, or a pump, or any combinations thereof.

9. The system of embodiment 8, wherein the pump is a manual pump or a piston pump.

10. The system of any one of embodiments 1 to 9, the air flow housing unit is configured to control the velocity, flow rate, direction and location of air flow out of the air flow housing unit.

11. The system of any one of embodiments 1 to 10, wherein the at least one air outlet is a plurality of air outlets.

12. The system of any one of embodiments 1 to 10, wherein the at least one air outlet is one outlet.

13. The system of any one of embodiments 1 to 12, where each outlet is a hole, an air nozzle, an air jet, or a slot, or any combination thereof.

14. The system of embodiment 13, wherein the hole is a flat hole or a formed hole.

15. The system of any one of embodiments 1 to 14, wherein the air source and the air flow housing unit form a single module within the system.

16. The system of any one of embodiments 1 to 14, wherein the air source and the air flow housing unit are separate, detachable modules.

17. The system of any one of embodiments 1 to 16, further comprising a power source, wherein the air source and the power source form an air-power unit.

18. The system of embodiment 17, wherein the air-power unit and the air flow housing unit are separate, detachable modules.

19. The system of embodiment 17 or 18, wherein the power source is a battery.

20. The system of embodiment 19, wherein the battery is a rechargeable battery.

21. The system of embodiment 17 or 18, wherein the power source provides grid powder or solar power, or any combination thereof.

22. The system of any one of embodiments 1 to 21, wherein the air housing unit receives pressurized air at the top of the air housing unit.

23. The system of any one of embodiments 1 to 21, wherein the air housing unit receives pressurized air at the bottom of the air housing unit.

24. The system of any one of embodiments 1 to 21, wherein the air housing unit receives pressurized air at the side of the air housing unit.

25. The system of any one of embodiments 1 to 24, wherein each air outlet has a diameter between 0.05 mm and 20 mm.

26. The system of any one of embodiments 1 to 25, wherein the system outputs air at:

-   -   (a) an air flow rate between 0.01 m³/min and 100 m³/min;     -   (b) an air pressure between 1 mm-H₂O and 1000 mm-H₂O; or     -   (c) an outlet air velocity between 0.1 m/s and 10 m/s, or any         combination of (a)-(c).

27. The system of any one of embodiments 1 to 26, wherein the air flow housing unit is configured to hold solid fuel on the top surface of the air flow housing unit, above at least a portion of the at least one air outlet.

28. The system of embodiment 27, wherein the solid fuel comprises biomass.

29. The system of embodiment 27, wherein the solid fuel comprises wood or charcoal, or any combination thereof.

30. The system of embodiment 27, wherein the solid fuel comprises urban waste or agricultural waste, or a combination thereof.

31. The system of embodiment 30, wherein the urban waste comprises paper, cardboard, or sawdust, or any combination thereof.

32. The system of embodiment 30, wherein the agricultural waste comprises animal processing waste, or cellulosic materials, or any combination thereof.

33. A combustion apparatus, comprising:

-   -   a combustion chamber; and     -   an air flow control system of any one of embodiments 1 to 32,         wherein at least a portion of the air flow housing unit in the         air flow control system is positioned inside the combustion         chamber and the air flow housing unit holds solid fuel on the         top surface of the air flow housing unit.

34. The apparatus of embodiment 33, wherein the apparatus is a cooking apparatus.

35. The apparatus of embodiment 33 or 34, wherein the apparatus has:

-   -   (a) an average high power thermal efficiency of at least 30%;     -   (b) an average high power carbon monoxide level of less than 2         g/MJd; or     -   (c) an average high power particular matter level of less than         100 mg/ML; or any combination of (a) to (c).

36. A method for burning solid fuel using a combustion apparatus of any one of embodiments 33 to 35, comprising:

-   -   placing solid fuel on the air flow housing unit of the air flow         control system in the combustion apparatus, wherein at least a         portion of the solid fuel is placed over at least a portion of         the air outlets on the air flow housing unit;     -   igniting at least a portion of the solid fuel;     -   turning on the air source to (i) provide air through the air         flow housing unit, and (ii) output the air through the plurality         of air outlets on the air flow housing unit; and creating a fire         from burning of the solid fuel.

EXAMPLES

The following Examples are merely illustrative and are not meant to limit any aspects of the present disclosure in any way.

Example 1 Performance Comparison in Cook Stove With and Without Air Flow Control System

This example compares the effect of using an air flow control system in a cook stove, with respect to fuel use, cooking power and emissions of the stove.

A wood stove was used in this example. The setup of the cook stove and air flow control system is depicted in FIGS. 8A-8E. A flat bottom pot was used in all tests. The pot dimensions were 24 cm in diameter, and 16 cm in height. The stove was first tested without the use of the air flow control system (Stove 1; Tests 1, 2, 3). The stove was tested again without the use of the air flow control system, but the stove was modified to operate in the natural draft operating mode, which included using a smaller diameter riser tube and shorter pot supports (Stove 2; Tests 4, 5, 6). The stove was then tested with the air flow control system in the forced draft mode (Stove 3; Tests 7, 8, 9), where the air flow rate was approximately 0.17 m³/min and the air pressure was 10 mm-H₂O. The air source was positioned on the bottom of the air flow housing unit as illustrated in FIG. 8A. Air was injected into the bottom of the stove via 62 holes (2 mm diameter) that were evenly spaced throughout the bottom of the combustion chamber. The air was driven by a fan operated at 12V.

During all of the tests at high power, the stove was fed with three pieces of Douglas Fir cut to the dimensions of 3.8 cm×4.5 cm×40-60 cm. At low power, it was fed with two of those sticks. In all cases the fuel had a moisture content of 10% (wet basis). For the natural draft configuration, the pot was filled with 2.5 L of water. For the forced draft configuration, it was filled with 5 L of water since it had a higher thermal efficiency.

The opening of the fuel door was 150 mm by 110 mm. The diameter of the riser tube was 150 mm. The pot supports were 20 mm high. The diameter of the riser tube was reduced to 100 mm. The height of the pot supports was reduced to 10 mm.

The results are summarized in Tables 1-3 below. Measurement details can be found in The Water Boiling Test Version 4.2.3 (released Mar. 19, 2014).

TABLE 1 Results for Stove 1 Metric Test 1 Test 2 Test 3 Average COV High Power Thermal Efficiency (%) 20.8 20.7 19.4 20.3 4% Low Power Specific Consumption (MJ/min/L) 0.110 0.102 0.106 5% High Power Carbon Monoxide (g/MJ_(d)) 7.75 5.77 4.16 5.89 30%  Low Power Carbon Monoxide (g/min/L) 0.35 0.39 0.37 6% High Power Particulate Matter (mg/MJ_(d)) 478.8 548.8 447.3 491.6 11%  Low Power Particulate Matter (mg/min/L) 17.68 22.92 20.30 18%  Indoor Emissions Carbon Monoxide (g/min) 0.53 0.60 0.56 8% Indoor Emissions Particulate Matter (mg/min) 31.7 35.2 33.5 7%

TABLE 2 Results for Stove 2 Metric Test 4 Test 5 Test 6 Average COV High Power Thermal Efficiency (%) 24.2 27.5 27.9 26.5  8% Low Power Specific Consumption (MJ/min/L) 0.227 0.173 0.177 0.192 16% High Power Carbon Monoxide (g/MJ_(d)) 2.83 3.08 2.62 2.84  8% Low Power Carbon Monoxide (g/min/L) 0.34 0.30 0.37 0.34 10% High Power Particulate Matter (mg/MJ_(d)) 277.3 247.1 245.8 256.7  7% Low Power Particulate Matter (mg/min/L) 20.08 15.01 14.48 16.52 19% Indoor Emissions Carbon Monoxide (g/min) 0.32 0.33 0.39 0.35 11% Indoor Emissions Particulate Matter (mg/min) 18.9 16.3 15.1 16.8 12%

TABLE 3 Results for Stove 3 Metric Test 7 Test 8 Test 9 Average COV High Power Thermal Efficiency (%) 37.5 38.4 36.4 37.4  3% Low Power Specific Consumption (MJ/min/L) 0.079 0.045 0.052 0.059 30% High Power Carbon Monoxide (g/MJ_(d)) 1.03 1.39 1.04 1.15 18% Low Power Carbon Monoxide (g/min/L) 0.08 0.11 0.09 0.09 12% High Power Particulate Matter (mg/MJ_(d)) 58.5 58.5 79.4 65.5 18% Low Power Particulate Matter (mg/min/L) 2.00 2.31 2.41 2.24 10% Indoor Emissions Carbon Monoxide (g/min) 0.31 0.40 0.31 0.34 16% Indoor Emissions Particulate Matter (mg/min) 7.3 8.8 8.6 8.2 10%

As can be seen from the results above, the use of Stove 3 (which included the air flow control system) was unexpectedly observed to perform better overall. 

What is claimed is:
 1. An air flow control system, comprising: an air source configured to output pressurized air; and an air flow housing unit having an interior, and a top surface with at least one air outlet, and wherein the air flow housing unit is configured to (i) receive pressurized air from the air source, and (ii) release air from the interior to exterior of the air flow housing unit through the at least one air outlet.
 2. The system of claim 1, wherein the air flow housing unit is connected to the air source by a connector, wherein the connector is rigidly or flexibly attached to the air flow housing unit, wherein the connector is optionally a hose or a joint.
 3. The system of claim 1, wherein the air source is a fan, a compressed air container, a pump, or an air bag, or any combination thereof.
 4. The system of claim 1, wherein the air flow housing unit is configured to control velocity, flow rate, direction and location of air flow out of the air flow housing unit.
 5. The system of claim 1, wherein each outlet is a hole, an air nozzle, an air jet, or a slot, or any combination thereof.
 6. The system of claim 1, wherein the air source and the air flow housing unit form a single module within the system or are separate, detachable modules.
 7. The system of claim 1, further comprising a power source, wherein the air source and the power source form an air-power unit.
 8. The system of claim 7, wherein the air-power unit and the air flow housing unit are separate, detachable modules.
 9. The system of claim 7, wherein the power source is a battery, rechargeable battery, grid power, or solar power, or any combination thereof.
 10. The system of claim 1, wherein the air flow housing unit receives pressurized air at the top surface of the air flow housing unit.
 11. The system of claim 1, wherein the air flow housing unit has a bottom surface, and wherein the air flow housing unit receives pressurized air at the bottom surface of the air flow housing unit.
 12. The system of claim 1, wherein the air flow housing unit has one or more side surfaces, and wherein the air flow housing unit receives pressurized air at the one or more side surfaces of the air flow housing unit.
 13. The system of claim 1, wherein each air outlet has a diameter between 0.05 mm and 20 mm.
 14. The system of claim 1, wherein the system outputs air at: (a) an air flow rate between 0.01 m³/min and 100 m³/min; (b) an air pressure between 1 mm-H₂O and 1000 mm-H₂O; or (c) an outlet air velocity between 0.1 m/s and 10 m/s, or any combination of (a)-(c).
 15. The system of claim 1, wherein the air flow housing unit is configured to hold solid fuel on the top surface of the air flow housing unit, above at least a portion of the at least one air outlet, wherein the solid fuel comprises biomass, wood, charcoal, urban waste, or agricultural waste, or any combination thereof.
 16. A combustion apparatus, comprising: a combustion chamber; and an air flow control system, comprising: an air source configured to output pressurized air; and an air flow housing unit having an interior, and a top surface with at least one air outlet, and wherein the air flow housing unit is configured to (i) receive pressurized air from the air source, and (ii) release air from the interior to exterior of the air flow housing unit through the at least one air outlet, wherein at least a portion of the air flow housing unit in the air flow control system is positioned inside, below, or near the combustion chamber, and the air flow housing unit holds solid fuel on the top surface of the air flow housing unit.
 17. The apparatus of claim 16, wherein the apparatus is a cooking apparatus, a cook stove, a manufactured stove, a traditional mud and ceramic stove, or a three stones fire, or any combination thereof.
 18. The apparatus of claim 16, wherein the apparatus has: (a) an average high power thermal efficiency of at least 30%; (b) an average high power carbon monoxide level of less than 2.5 g/MJd; or (c) an average high power particulate matter level of less than 250 mg/ML; or any combination of (a) to (c).
 19. The apparatus of claim 16, wherein the apparatus has: (a) an average high power thermal efficiency at least 40% higher; (b) an average high power carbon monoxide level at least 50% lower; or (c) an average high power particulate matter level at least 70% lower; than when using the combustion apparatus without the air flow control system.
 20. A method for burning solid fuel using a combustion apparatus of claim 16, comprising: placing solid fuel on the air flow housing unit of the air flow control system in the combustion apparatus, wherein at least a portion of the solid fuel is placed over at least a portion of the air outlets on the air flow housing unit; igniting at least a portion of the solid fuel; turning on the air source to (i) provide air through the air flow housing unit, and (ii) output the air through the plurality of air outlets on the air flow housing unit; and creating a fire from burning of the solid fuel. 